Kuwata
Chemistry 311
Fall 2007
Chapter 5 Example Problem—Vapor Pressure Lowering
The vapor pressure of (pure) water at 20.0°C is 17.535 Torr. Consider a solution in
which 30.00 g of lithium sulfate (M = 109.95 g mol-1) is completely dissolved in 500. g
of water (M = 18.02 g mol-1). Assume that Raoult’s Law applies to the solution.
(a)
(b)
(c)
Predict the vapor pressure of the aqueous lithium sulfate solution at 20.0°C.
Careful measurements with an isoteniscope reveal that the actual vapor pressure
of the aqueous lithium sulfate solution at 20.0°C is 17.074 Torr. What is wrong
with our calculation in part (a)?
What is wrong (or at least overly simplistic) with our refinement in part (b)?